The present invention generally relates to damping devices and, more particularly, relates to a tuned mass damper for damping oscillations and vibrations which occur in structures, such as those found on spacecraft satellites.
Certain types of structures oscillate when subjected to vibratory excitations. Examples of vibration excitable structures include reflectors, solar arrays, and booms for carrying equipment, all of which are commonly found on spacecraft satellites which are subjected to thermal shocks and other vibratory excitations that may cause the structure to vibrate at a predetermined frequency. Vibratory oscillations of these and other structures can cause inaccuracy in equipment associated therewith and, thus, it is desirable to damp vibrations in certain structures.
Conventional tuned mass dampers generally employs a spring positioned proof mass mounted in a container of damping fluid. The spring stiffness and the mass are chosen to have substantially the same frequency of oscillation of the structure and damper device combination so that, upon oscillation, the vibrating structure provides an input to the damper. Due to the damper arrangement, the mass vibrates one hundred eighty degrees (180xc2x0) out of phase with the vibrating structure. As a consequence, the tuned mass damper essentially absorbs a substantial portion of the energy of the vibrating structure and cancels the structure motion at the predetermined frequency so that the tuned mass damper and structure begin to vibrate at two slightly different off-resonant frequencies. As a consequence of the resultant damping, the displacement of the vibrating structure is substantially reduced.
Many conventional tuned mass dampers employ a proof mass that is limited to damping vibrations in a single axis. One approach to providing multiple-axes damping is disclosed in U.S. Pat. No. 5,775,472, entitled xe2x80x9cMULTI-AXIS TUNED MASS DAMPER,xe2x80x9d the disclosure of which is hereby incorporated herein by reference. The aforementioned approach employs a single mass mounted for motion in two or three axes and supported by springs chosen to provide a frequency of vibration in each axis. In each orthogonal axis, a pair of oppositely directed expandable bellows containing a damping fluid are connected between wall portions of a generally cylindrical cup-shaped housing and the mass to permit motion of the mass along the designated axis. While multiple pairs of bellows and springs are arranged to achieve damping in multiple orthogonal axes, the spring and bellows design of the above-described tuned mass damper offers limited translational movement of the mass.
It is therefore desirable to provide for a tuned mass damper which permits large translational deflections of the proof mass. In particular, it is desirable to provide for a multi-axes tuned mass damper which allows extended movement of the mass in directions transverse to the individual primary orthogonal damping axes.
The present invention provides for a multiple axes tuned mass damper which permits extended transverse movement of a proof mass. The tuned mass damper includes a container having inner walls and a mass disposed within the container. The damper has a first pair of oppositely directed fluid containment assemblies each including a cup-shaped containment member and an expandable bellows connected to the mass to define a fluid chamber containing a damping fluid. The first pair of oppositely directed fluid containment assemblies permit motion of the mass along a first axis. The damper also has a second pair of oppositely directed fluid containment assemblies each including a cup-shaped containment member and an expandable bellows connected to the mass to define a fluid chamber containing a damping fluid. The second pair of oppositely directed fluid containment assemblies permits motion of the mass along a second axis. First and second springs bias the first pair of fluid containment assemblies between opposite inner walls of the container. The first and second springs each have an outside diameter less than an inside diameter of the cup-shaped containment members to allow translational deflection of the mass about an axis other than the first axis. Third and fourth springs bias the second pair of fluid containment assemblies between opposite inner walls of the container. The third and fourth springs each have an outside diameter less than an inside diameter of the cup-shaped containment members to allow translational deflection of the mass about an axis other than the second axis.